1. Field of the Invention
The present invention relates to exhaust gas purifying apparatuses for internal combustion engines (hereinafter referred to as "engines") to be used in automobiles or the like.
2. Description of the Prior Art
Regulations for exhaust gas of automobiles are becoming stricter year by year. Particularly, it is becoming more and more severely requested to decrease noxious contents in exhaust gas, such as carbon monoxide CO, hydrocarbons HC, nitrogen oxides NO.sub.x or the like, by purifying the exhaust gas discharged immediately after starting up and before completion of warming up of engines. As a countermeasure therefor, there has been known an exhaust gas purifying apparatus to be mounted on the exhaust port of the engine, which comprises a first exhaust converter having a small capacity and a second exhaust converter having a large capacity, for converting the noxious contents into innoxious components. In such an exhaust gas purifying apparatus, the noxious contents are decreased by the first exhaust converter wherein a high temperature is readily attained and thereby a catalyst is rapidly activated, mainly immediately after starting up and before completion of warming up of the engine and then by the second exhaust converter having a larger capacity after the warming up of the engine has been completed. Among these exhaust gas purifying apparatuses, some have been designed to feed air at an appropriate feed rate into exhaust gas to improve an exhaust gas purification efficiency.
However, in the above-mentioned exhaust gas purifying apparatus there has been posed a problem such that since the first exhaust converter comprises a catalytic substrate having a heat capacity not small enough to sufficiently activate the catalyst while the engine is under the condition between immediately after starting up and before completion of warming up, a good exhaust gas purification efficiency cannot be obtained. In this specification, the term "heat capacity" is meant by a heat capacity of a catalytic substrate including exhaust flow passages formed therein (hereinafter, the exhaust flow passage is referred to as "cell").